1. Field of the Invention
The present invention concerns a process for aligning and centering an assembly of electron-guns on a color television tube. It also concerns a device to carry out the process according to the invention.
A classic color television tube comprises a glass shell or envelope of which the enlarged end supports a screen. It also comprises a neck facing the screen that supports an assembly of electron-guns. This assembly is constituted by a disposition of thermoelectronic cathodes and electrodes, for example, an in line or delta-wise disposition. It constitutes a mechanical entity that must be inserted on the tube, by its neck, with a maximal precision with respect to both rotation and position relative to the central axis of the tube. It thus concerns the insertion of the assembly of guns with a positioning error as low as possible.
2. Description of the Prior Art
Different means are known in the prior art for measuring the placing error, prior to sealing of the assembly of guns to the tube. Among those are mechanical devices of the so called feelers type, image superimposition devices and devices using the intensity variation of a transmitted or reflected luminous beam which are especially known. A description of these devices will be found in French patent published under No. 2 341 937. The present invention proposes a simple means, relatively insensitive to errors, for supplying position data able to be immediately used by an automatic adjustment system. Indeed, the alignment processes using optical intensity measurements are affected by imprecisions due to noise and to the difficulty of appreciating intensity maximums.
With this aim, the present invention concerns a process for aligning and centering an assembly of electron-guns on a color television tube. In such a process, the angle between a first direction corresponding to the direction of the assembly of guns and a second reference direction is cancelled or rendered void. In the process according to the invention, beam is formed on at least one optical analyzer a contrasted image with sharp edges of a section of the assembly of guns. The measurement of the position of the image on the analyzer is a measurement of the placing error that is cancelled by the displacement of the assembly of guns.
The present invention also concerns a device for carrying out the process described herein above. The device according to the invention comprises at least one optical analyzer along a reference direction mounted on a support, the analyzer supplying a measurement of the placing error that is cancelled by the displacement of the assembly of guns to be mounted on the neck of a television tube.
One advantage of the present invention is to allow an easy adaptation to assemblies of guns of different types. In particular, it allows the mounting of guns that bear optical markings, reflecting patches or wallholes.
Another advantage of the invention is to supply distinct data for the centering and aligning. Indeed, it will be observed that if the axis of the assembly of guns does not coincide, i.e. is non-centered with the axis of the tube, it will be observed on two optical analyzers, that a dissymmetry of images as well as a shift due to an alignment defect representing an angular shift of the assembly of guns about its axis occur .